A bi-fuel internal combustion engine is capable of running on two or more different types of fuel. Modern bi-fuel engines utilize different fuel injectors for each type of fuel. For example, a bi-fuel engine may include a fuel system that utilizes separate liquid and gaseous fuel injectors for each cylinder of the engine. The use of multiple fuel types may provide performance benefits over a variety of different operating conditions. However, improper operation of the electrical relays for the injectors may negatively affect vehicle performance. For example, if the contacts of an electrical relay become stuck closed, the engine may receive double fueling. Because these relays are an important part of proper engine operation, on board diagnosis is important.
What is needed, therefore, is a system and method for diagnosing proper operation of an electrical relay that controls power to a fuel injector. What is also needed is a system and method for performing this diagnosis that does not increase cost or complexity of the fuel injector relay circuitry.